Personal defense weapon

Personal defense weapons (PDWs) are compact magazine-fed automatic firearms, typically performing as a submachine gun designed for secondary defensive use rather than as a primary service weapon. Some PDWs fire a small-caliber (generally less than 8 mm or 0.31 in in bullet diameter), high-velocity centerfire bottleneck cartridge resembling a scaled-down intermediate cartridge, essentially making them an "in-between" hybrid between a submachine gun and a conventional carbine assault rifle. The name describes the weapon's original conceptual role: as a compact but powerful small arm that can be conveniently carried for personal defense, usually by support personnel behind the front line such as military engineers, logistic drivers, medical specialists, artillery crews, or signallers. These "second-line" personnel are not strictly combat troops expected to directly engage the enemy, but may still be at risk of encountering decently equipped (and often well-armored) hostile skirmishers and infiltrators, therefore having to defend themselves in close quarters. Such encounters were thought to warrant an effective weapon that would have sufficient range for engagements that exceed handgun capabilities, but without the unnecessary bulk of a full-sized service rifle causing a burden during their normal duties. However, the concept has generally proven unsuccessful for this application, with carbines still being widely preferred for these roles.